1. Field of the Invention
This invention relates generally to controlling hydraulic fluid flow that lubricates a rotating clutch and discontinues the flow when the clutch is not rotating.
2. Description of the Prior Art
In an automatic transmission certain control elements, such as hydraulically-actuated clutches, are engaged and rotating only during operation in a few speed ratios and are non-rotating in the other speed ratios. When rotating they must be supplied with hydraulic lubricant at a flow rate of approximately 0.7 liters/minute. But if the flow rate is continuous during period of their non-rotation, energy is wasted and required pumping capacity is unnecessarily higher. Reducing pump flow demand improves fuel economy.
Furthermore, supplying oil flow to the clutch when it is stationary causes oil puddling, which can cause stick-slip performance problems.
A need exists in the industry for a technique that provides lubricant flow to such clutches only during periods of non-rotation without requiring computer-control or a need for an electronic solenoid for actuation.